Metal-core weld wires are generally composite tubular filler metal electrodes having a metal sheath and a core composition formed of various powdered materials. As compared to flux-cored wires, metal-core wires have a core composition comprising primarily of metallic and alloying powders with substantially reduced amounts of fluxing agents.
During the manufacture of metal-core wires, the core composition is commonly blended and deposited onto a steel strip, which is formed into a tube, or sheath, about the core composition in a forming mill. The steel sheath surrounding the core composition is then drawn through reducing dies to a specified diameter, and any lubricants accumulated onto the exterior of the wire can be removed in a baking process; however, this is not required.
Metal-core wires are used increasingly as an alternative to solid weld wires for improved productivity in structural fabrication. Metal-core wires can have increased weld deposition rates and produce wider, more consistent penetration profiles than solid wires. Metal-core wires can also generate less spatter, provide improved arc stability and produce weld deposits with an improved wetting characteristic in comparison to solid wires.
Metal core wires are increasing used in the welding of metal pipe. When welding larger metal pipe, it is becoming more common to form a weld bead in a narrower groove having a width of about 8-20 mm. The narrower groove allows for a single pass in each layer of weld metal. As such, faster welding times and smaller weld beads are achieved. However, when forming a weld bead in a narrow groove, the cooling rate of the weld bead is generally faster due to the lower heat input when forming the weld bead. These faster cooling rates of the weld metal can result in a weld bead having increased yield and tensile strengths, but reduced fracture toughness. As such, a weld bead having such reduced properties can result in it cracking and/or breaking from the metal pipe, thus severely compromising the integrity of the welded joint.
Prior art metal cored electrodes have been formulated to increase the impact strength properties of the weld metal. One such metal cored electrode is disclosed in U.S. Pat. No. 5,824,992, which is incorporated herein by reference.
Although advancements have been made in the prior art regarding metal cored electrodes, there remains a need in the art for a metal cored electrode that can form a weld with improved toughness at high yield and tensile strengths.